Re: pluggable out-of-date (Was: non-recursive build question)

[Noel Yap]

There's a few of issues with this solution:
- it's conceivable that out-of-date calculations may want to be done on a 
per-rule basis
- even if it's on a per-project basis, a per-make calculator is still too 
course-grained
- I've seen some really nasty problems with Linux's loader

Having said this, I do agree that a pluggable interface is the way to go.  I 
don't know GUILE (yet) but I'm hoping GUILE support along with a GNU make hook 
will allow this feature.

Noel

David Boyce wrote:

> It's always struck me that the best way to answer the out-of-date 
> question generically is via a "plugin" design. Any implementation that's 
> hardwired into make is bound to be wrong for someone's needs. Couldn't 
> make do something like this: at startup, it uses the dlopen/dlsym() 
> interface (there's something similar on Windows) to look for a function 
> with a particular name and a documented signature including a boolean 
> return value. If found, that's what it uses to make subsequent 
> out-of-date decisions. If not (the normal case), it falls back to an 
> internal function which simply implements the forward-timestamp-based 
> logic that's always been standard.
>
> This would allow for alternate implementations of statefulness, entirely 
> configurable by the client site. Developers would only need create a 
> shared library implementing the documented function. They could then 
> build gmake so as to link it in explicitly, or LD_PRELOAD it on an 
> as-needed basis. I could see a whole cottage industry of plugins 
> developing.
>
> One limitation is that GNU make has probably been ported to some old 
> platforms which don't have dlopen/dlsym or similar. But IMHO it wouldn't 
> be so bad to make this feature depend on a HAVE_DLFCN_H configure macro 
> and thus be available only on modern platforms, which all support 
> something similar AFAIK. Certainly SUS specifies dlopen.
>
> Would this work or am I misunderstanding something about dlopen?
>
> -dsb